No faction in bannerlord is a one to one copy of a RL one, Vlandia isn't Normandy but a conglomerate of medieval themes with a strong central point of Norman influence, same goes for every other faction.
I agree it would be cool to have the Nords themselves starting their famous invasion of Calradia we hear about in warband but you don't need to deny that the Sturgians are a mix of Rus with a Norse elite for that, this is their very lore, Nord warlords intermarrying and ruling over the native Sturgian population of northern Calradia.
They would have to change or advance the lore a bit though, i know of one Nord companion in the game that tells us how his/her homeland is divided among squabbling warlords raiding each other for petty things and after the neighboring tribe sacked their own without any provocation, the survivors left for Calradia and he/she won't return saying that it's better to live under the protection of any king, even a tyrant, than returning to that lawlessly place.
edit: also a small pet peeve of mine, viking is a profession and not a people, that means more or less pirate. The Scandinavian peoples went viking in the summer to provide a better income for their families and tribes, some raided, some traded and some did both in a single "viking season".